Effect of Grain Size and Structure on Carbon-Molybdenum Steel Pipe: An Investigation of These Properties for Their Bearing on Suitability of Such Pipe for High-Temperature Steam Service

Abstract

Abstract This paper gives the results of an investigation sponsored by The Detroit Edison Company at the University of Michigan for the purpose of relating the grain size and grain structure of carbon-molybdenum steel pipe to its high-temperature creep properties at 925 F. Pipe specimens were obtained from eight different heats of carbon-molybdenum steel, six being made by the open-hearth, and two by the electric-furnace process, and an attempt was made to correlate the respective creep strengths at 925 F with other significant properties obtained through short-time tests. At this stage of the investigation no apparent relationship was found. Further tests were conducted on heat-treated specimens from a single heat of steel which had been made by a preferred melting practice. From these tests, it is evident that, if the carbide structures are of a Widmanstätten type, with grain sizes ranging from 2 to 7, the steels will have high-temperature creep properties superior to those in which the carbides are in other conditions or forms. It is also believed that too great an emphasis has been placed on grain size and not enough on type of carbide structure. It is felt that consideration should be given to both factors, though with greater emphasis on the type of carbide structure.